Most headphones available on the market today produce an in-head sound image when driven by a conventionally mixed stereo signal. “In-head sound image” in this context means that the predominant part of the sound image is perceived as being originated inside the listeners head, usually on an axis between the ears. If sound is externalized by suitable signal processing methods (externalizing in this context means the manipulation of the spatial representation in a way such that the predominant part of the sound image is perceived as being originated outside the listeners head), the center image tends to move mainly upwards instead of moving towards the front of the listener. While especially binaural techniques based on HRTF filtering are very effective in externalizing the sound image and even positioning virtual sound sources on most positions around the listeners head, such techniques usually fail to position virtual sources correctly on a frontal part of the median plane (in front of the user). This means that neither the (phantom) center image of conventional stereo systems nor the center channel of common surround sound formats can be reproduced at the correct position when played over commercially available headphones, although those positions are the most important positions for stereo and surround sound presentation.